1. Field of the Invention
The invention relates to an interrogation-answering system in connection with a primary radar, whereby an interrogation station transmits interrogation signals with a certain interrogation code, which signals are answered by an answering station with a certain answering code.
2. Description of the Prior Art
For the utilization with primary radar devices it is know to make use of the so-called pulse compression (Skolnik "Radar Handbook", 1970, Chapter 20-2 to 20-36). The echo signals, which are received by the reflection from a target, are subjected to an auto-correlation and result in amplified echo signals corresponding to the compression factor. In detail, the coding of the transmitting signals is performed by frequency or phase modulation and the compression networks are designed in accordance with the kind of modulation used at the transmitting end.
Experiments have become known (Electronic Engineering, July 1961, page 416, as well as in the "Proceeding of the IEE", Vol 112, No. 5, May 1965, pages 861 and 862) in which cases the interrogation signals for a transponder were transmitted by the primary radar transmitter. During the "Interrogation" by the primary radar transmitter, a single pulse is transmitted while the answering signals were coded in a corresponding pulse succession. Due to the lack of the possibility of a selective coding in generating the interrogation signal in the primary radar transmitter and due to the therewith connected undesired starting of answering signals by other primary radar devices which were not at all connected to the respective system, these proposals were considered unsuited and were not further pursued.
In combined primary and secondary radar systems, a special transmitter for the primary radar device and a special transmitter for the secondary radar device is always provided. This results in great expenditures which are not reasonable, particularly not for smaller or mobile systems.